VALVE EVENT DURATION CONTROL VIA SECONDARY CLOSING

CAMSHAFT WITH PHASER

FIELD OF THE INVENTION

The improved concept pertains to the field of engine valve actuation systems. More particularly, it pertains to an improved system for controlling the duration of the valve event for engines having multiple controlled valves.

DESCRIPTION OF RELATED ART

In many types of internal combustion engines, such as spark ignition engines and diesel engines, valves are used to control the flow to and from the variable volume chamber of each cylinder. These valves are conventionally operated in timed relationship to the output or drive shaft so that valves open and close at specific times in the cycle of operation.

The operation of internal combustion engines often causes the generation of undesirable emissions. These emissions include particulate matter and nitrous oxide ("NOx") which are generated when fuel is ignited in the combustion chamber of the engine. The exhaust stroke of the engine forces these emissions into the environment. It is desirable to control the valve cycle ("valve event") to minimize the amount of these undesirable emissions.

With internal combustion engines, the timing of the valve opening and closing may be varied in order to obtain optimum performance in response to inputs from sensors that monitor the operating parameters of the engine. For example, it is desirable under high speed, high load conditions to maintain a long period when the valve is in an open condition and exhibit a rapid rate of opening and closing in order to improve volumetric efficiency and increase engine output. But, such valve timing provides generally poor

running conditions under low speed, low load conditions. The reason is that in order to obtain maximum power output, it is necessary to charge the combustion chamber with the maximum possible amount of combustion ingredients (e.g. fuel and air mixture). However, when running at low speeds and low loads, long valve opening intervals reduce the amount of inducted charge due to flow reversals at the beginning and/or end of the valve lift event.

It is well known in diesel and spark ignition engine technology that by controlling the duration that an intake valve is open, the effective power developed by the engine during each piston stroke can be changed. Both timing and intake opening and closing can have significant effects on power and emissions, depending on engine speed and load.

Additional uses of varied intake and exhaust valve events include the control of emissions from spark-ignition and diesel engines, mainly through control of internal Exhaust Gas Residuals, and the enabling of alternate modes of combustion such as HCCI and CAI.

Both spark ignition and diesel engines typically use a camshaft to control the opening and closing of intake and exhaust valves. The open period of the valves is referred to as "duration" or "dwell" and is determined by the fixed shape of the lobes of the cams. The shape of lobes of these cams establishes the primary valve event control duration. This cam lobe profile cannot be varied without replacing the camshaft with another having a different lobe or "ramp" profile for the cams.

On engines that have variable camshaft timing, the opening and closing points of the valves can be varied but the actual duration or dwell of the valve opening remains fixed. While this is of some use for performance and efficiency enhancement, as well as improving emissions, the degree of improvement is limited compared to a system that can also adjust the valve-event duration.

It has been regarded for some time as being highly desirable to design camshaft operating systems that vary the duration of the valve opening in order to maximize engine torque throughout a wider range of engine operating conditions. The principal advantage of such a variable valve event system is to improve the torque spread of the engine. An

added benefit is the minimization of intake pumping losses coupled with lower exhaust emissions. However, as previously discussed, the modification of the timing of a valve system that is driven by a cam device is determined by the shape of the lobe of the cams. Since the shape of the cam is fixed, there will be engine operating conditions where the optimal solution for valve opening and closing cannot be obtained.

Attempts have been made to vary the duration of the valve event to maximize torque requirements and contribute to a reduction in emissions. U.S. Patent No. 5,178,105 to Norris, discloses a valve gearing device for internal combustion engines using two cams rotating about two separate but parallel shafts. Each cam contacts one side of a triangularly shaped "follower" positioned on the upper surface of each engine valve tappet. A cam phasing device is used to vary the phase of one of the cams relative to the other. The cam lobes have ascending and descending portions (or "ramps") that, in combination, adjust the position of the follower in response to phase changes. The movement of the follower on the surface of the tappet controls the timing and duration of the opening and closing of the valve.

Another approach is presented by Hussani et al. in WO 94/28288. They disclose a valve timing control device that also employs two camshafts. A hydraulic actuator interacts with the main camshaft to impart a periodic stroke to open and close each valve according to a pre-set cam profile. A second, or control, camshaft interacts with a pressure relief device on the hydraulic actuator. The second camshaft is controlled by a phasing device mounted at its driven end. In response to phase changes, the second camshaft regulates the discharge of hydraulic fluid from the actuator, thus modulating the duration of the valve opening.

With specific reference to diesel engines, U.S. Patent No. 7,044,122, Cornell et al., discloses a system to control the "Miller" cycle. The system implements a late intake

Miller cycle in which the intake valves are held open during a portion of the compression stroke. A standard cam mechanism axially moves an actuator rod which engages one end of a rocker arm. The rocker arm pivots at its approximate mid point while one end contacts the stem of an intake valve to urge the valve to open and close in response to the rotation of the cam. A microprocessor monitors engine operating conditions and controls

a hydraulic fluid actuator chamber, which in turn, urges an actuator rod into engagement with the rocker arm to hold the intake valve in the open position for a longer duration, as desired. The actuator rod operates independently from the action of the primary cam.

U.S. Patent No. 7,011,056, Melchior, discloses two parallel camshafts, each one operating either the intake valves or the exhaust valves of an engine. Cams on each camshaft operate in tandem to advance or retard the opening and closing of each valve. A phasing device located at the front end of at least one of the camshafts regulates the phase angle between the two camshafts. Each valve is actuated by pressurized hydraulic fluid that is contained within a pressure chamber. A piston attached to the end of the valve stem controls the movement and location of the valve in response to changes in the pressure of the hydraulic fluid in the chamber during the valve cycle. Depending on the phase angle, both cams operate in tandem to either increase or decrease pressure in the pressure chamber. Increased pressure will keep the piston from retracting, which in turn, maintains the valve in the open position. The cams cannot operate independently. They are designed to cooperate with each other to control the duration of the valve event.

One disadvantage of the systems previously described is that these dual shaft cam mechanisms control the valve event in concert with each other. The effect on the valve event by both cam devices is additive, that is, the net valve motion is the summation of the two cam lobes. It is desirable to have independently operating cams so that if varying the valve event is unnecessary, the secondary cam does not interfere with the normal operation of the primary cam. A system of independently operating cams provides a simpler yet more efficient valve event control mechanism. Further, it is desirable to modify only the duration of the valve event while maintaining substantially full valve lift. This is not possible with the conventional summing mechanisms unless a pair of long- dwell cams are utilized. These types of cam lobes present significant valvetrain dynamics challenges, however. What is desired is a method to improve engine torque over a wider range of engine operating conditions while concurrently minimizing the production of undesired emissions.

SUMMARY OF THE INVENTION

Diesel engines, and to a lesser extent, spark ignition engines have a need to control the duration of the valve event while maintaining substantially full valve lift. The present concept achieves this and other objectives hereinafter described.

The improved valve event control system includes a primary camshaft that operates a valvetrain in the conventional way, such as by a pushrod cam-in-block, overhead camshaft end pivot, center pivot or direct acting tappet. This portion of the valvetrain provides the base valve motion to the valvetrain. The base valve motion curve is the shortest duration required by the engine, whether for the intake or the exhaust valves.

A secondary camshaft is placed in operative engagement with the valvetrain, acting either on the rocker arm or directly on the tappet, as dictated by the design of the valvetrain. The secondary camshaft provides a slightly lower lift and has a shorter duration valve motion curve. It is phased with respect to the primary camshaft by a conventional cam phasing device.

If the secondary camshaft is in the fully advanced position, it has no influence on valve motion, which is controlled by the primary camshaft. As the secondary camshaft is progressively retarded by a cam phasing device, it inhibits the motion of the valvetrain to close the valve, thereby extending the duration of the valve event. The duration of the open time of the valve is determined by the difference in the phase angle.

With respect to diesel engines, the advantages provided by the present invention are as follows. It extends the operating range of the homogeneous charge compression ignition ("HCCI") mode of combustion by controlling the time of the closing of the intake valve, thus optimizing the effective compression ratio. In addition to HCCI control, Miller or Atkinson cycle operation can be enabled. By varying the effective compression ratio, the ability to control NOx emissions is improved. Also, cold-start capabilities as well as compromises resulting from fixed valve event volumetric efficiencies throughout the entire range of engine speed are improved. When installed on the exhaust valvetrain, varying the duration of the opening of the exhaust valve reduces the amount of trapped exhaust gases, thus improving the efficiency of the HCCI mode of combustion over a broader range of operating conditions.

Varying the effective compression ratio can also improve cold start quality. If the exhaust valve opening timing is varied, engine efficiency and power output is improved by optimizing the effective expansion ratio and exhaust pumping capabilities.

A phasing device may also be added to the primary intake and/or exhaust camshaft to vary the effects of valve overlap and inertia cylinder charging throughout the full range of engine speeds.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a schematic representation of the improved valve event control mechanism installed on a conventional center pivot rocker arm valvetrain.

Fig. IA shows a top plan view of the cam arrangement of the improved valve event control mechanism above the cylinder head of a typical engine.

Fig. 2 shows a graph of the curve of the basic valve duration and lift compared to the extended duration effects of the improved device.

Fig. 3 shows a cam-in-block coupled with an overhead cam valvetrain.

Fig. 4 shows a dual cam-in-block valvetrain mechanism.

Fig. 5 shows a variation of the valvetrain mechanism of Figure 4 with the cams acting directly on the center pivot rocker arm.

Fig. 6 shows an end pivot rocker arm with two overhead cam devices.

Fig. 7 shows an overhead cam end pivot rocker arm with a bucket tappet.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows one embodiment of the valve event control device 10. A conventional valvetrain used within either a diesel or a spark ignition engine is shown. The valves shown in the appended Figures can be either intake or exhaust valves. Figure 1 shows a center pivot rocker arm valvetrain. This includes a valve 12 that is non- permanently engaged with a valve seat 14. The valve seat 14 separates passage 16 from

the combustion chamber 20 of cylinder 22. The volume of the combustion chamber 20 varies with the reciprocal motion of the piston 24 within cylinder 22. Passage 16 provides the route for the ingress of the combustible fuel mixture into the combustion chamber 20 for intake valvetrains or the route for the egress of exhaust gases after combustion for exhaust valvetrains.

The stem 18 of valve 12 is slidably disposed within a shaft 26 in the cylinder head 28 of the engine. A spring 30 acts upon a spring retainer 32, which is securely affixed to the shaft of stem 18, to default bias the valve 12 into full abutment with the valve seat 14. The upper end of valve stem 18 loosely abuts rocker arm 40 in proximity to a first end 42. Rocker arm 40 pivots about axis 46 substantially at a mid point between first end 42 and second end 44.

In one embodiment of the center pivot rocker arm valve control device 10 shown in Figure 1, the opening and closing of the valve 12 is controlled by a primary camshaft, which contains a plurality of integral cams as represented herein by primary cam 50. Primary cam 50 rotates about the axis 51 of the primary camshaft and has ascending 53a and descending 53d ramp portions terminating in an eccentric lobe 54. As the primary camshaft rotates about axis 51 in response to the rotation of the engine's driveshaft, the primary cam 50, in turn, rotates so that, as the ascending ramp 53a slides along the surface of the rocker arm 40, the rocker arm 40 pivots about its axis 46 and the valve stem 18 is urged downward which begins to open the valve 12. The maximum "lift" of the valve 12 is achieved when the lobe portion 54 of the primary cam 50 contacts the surface of the rocker arm 40. The valve 12 begins to progressively close and approach full engagement with the valve seat 14 as the primary camshaft continues its rotation and the descending ramp 53d progressively slides across the surface of the rocker arm 40.

Figure IA is top plan view of a schematic representation of the cylinder head of a typical engine. The cylinder head 28 contains a plurality of cylinders 22 (two are shown in this figure). Each cylinder has at least one intake and at least one exhaust valve 12. In order to simplify the description of the present invention, Figure IA only shows one valvetrain, which can be either an intake or exhaust valvetrain. Primary camshaft 55 is driven by sprocket 82, which in turn, is driven by a chain or belt that is connected to a

sprocket attached to the drive shaft (not shown) of the engine. The primary camshaft 55 contains a plurality of integral cams 50, each of which engages a pivotable rocker arm 40. Each rocker arm 40 contacts the valve stem (not shown) and directly controls the opening and closing of each valve 12. A secondary camshaft 72 also contains a plurality of cams 70, each of which engaging its respective rocker arm 40. The end of the secondary camshaft 72 may be connected to phasing device 85, which is driven by the belt or chain driven power transmission system of the engine. Alternative cam drive arrangements include the primary cam driving the secondary cam phaser, the primary cam phaser driving the secondary cam phaser or the secondary cam phaser being driven from the crankshaft or an idler sprocket of a multi-stage cam drive system.

The movement of the valve 12 with respect to time is shown in Figure 2. When the primary camshaft alone acts upon the valvetrain, the movement of the valve 12 is represented by the solid line sine wave 60. When the cam lobe 54 rotates to its point of full contact with the surface of the rocker arm 40, maximum valve lift occurs which is represented by the peak of the sine wave.

With specific reference to compression ignition engines, it is desirable to control the closing of the intake valve to improve volumetric efficiency compromises that occur throughout the entire range of engine operating conditions, aid in cold engine start up quality and reduce the amount of NOx emissions. This is best achieved by controlling the duration of the valve event by extending the opening of the intake valves. Referring again to Figures 1 and IA, the present invention achieves this by providing a separate, secondary, camshaft 72 to act upon the valvetrain. A secondary cam 70, which is integral with the secondary camshaft 72, is driven by the rotation of the secondary camshaft about axis 71. The secondary camshaft 72 is controlled by a conventional engine timing phasing device 85. Exemplary phasing devices include oil pressure actuated, torsion assist and cam torque actuated phasing mechanisms. These devices respond to inputs from the continuous monitoring of engine performance and emissions by at least one sensor and then accordingly adjust the phase angle between the primary camshaft and the secondary camshaft. If the engine is operating at optimum conditions, the phasing device will not alter the phase angle between the primary 55 and secondary 72 camshafts and the secondary camshaft 72 will have no effect on the valve event. If however, phase angle

adjustment is required, the phasing device 85 changes the phase angle between the two camshafts. When the phase angle of the secondary camshaft 72 is retarded with respect to the phase angle of the primary camshaft 55, the secondary cam 70 will rotate to prevent the rocker arm 40 from allowing the valve 12 to return to the valve seat 14, thus extending the duration of opening of the intake valve. The effect of the phase shifted secondary cam on the duration of the valve opening is represented by the phantom line 62 in Figure 2. The amount of time that the valve is held open is variable and is controlled by the phase angle difference as dictated by the phasing device.

The improved device may also be utilized with respect to the exhaust valves of a diesel engine. With reference again to Figure 1, assuming that the valvetrain shown is for an exhaust valve, the primary cam 50 controls the normal opening and closing of the valve 12. In response to phase angle changes dictated by the phasing device that is operatively engaged with the secondary camshaft, the secondary cam 70 prevents the closing of the exhaust valve for a period of time sufficient to alter the amount of exhaust gases remaining in the combustion chamber 20. By varying the amount of exhaust gases remaining after combustion, the valve event control device 10 extends the operating range of the homogeneous charge compression ignition mode of combustion.

Alternatively, the operation of the device can be mirror- imaged to have the secondary camshaft advance the valve opening time and therefore the valve event duration. This will be particularly useful in a Diesel engine where the exhaust opening is useful for controlling and extending the range of the HCCI mode of combustion.

Optionally, it may be desirable to add a phasing device to the primary camshaft of either the exhaust or intake valvetrains. The addition of a primary camshaft phasing device, coupled with a secondary camshaft phasing device, provides a limited degree of valve overlap control over and above the duration control that is provided by having only secondary camshaft phasing. This allows for the ability to vary the internal exhaust gas residual, as necessary.

In addition to being used with diesel engines, the improved valve event control device provides benefits to spark ignition engines. When installed on the intake valvetrains of these engines, by delaying the closing of the intake valve in response to

changing engine conditions and/or emission quality, the compression ratio within the combustion chambers of the cylinders can be varied to provide optimal operating conditions. Further, varying the duration of the opening of the intake valve in such engines improves cold engine start up quality as well as optimizing compromises made to fixed valve event volumetric efficiencies that occur throughout the full range of engine speeds.

Again with respect to spark ignition engines, installing the improved valve event control device on the exhaust valvetrain provides added benefits to the efficient operation of the engine. Varying the duration of the opening of the exhaust valves provides a means to optimize engine operating parameters and power output that are affected by the tradeoff between an effective expansion ratio and exhaust pumping efficiencies.

Optionally, a phasing device can be added to the primary camshaft of either or both of the intake or exhaust valvetrains to vary the degree of valve overlap control in addition to the duration control provided by the phasing device operating on the secondary camshaft. An added benefit of the addition of a primary camshaft phasing device is improved inertia cylinder charging throughout a wider range of engine speeds.

An alternate valvetrain mechanism is shown by the schematic representation in Figure 3. The valvetrain is an overhead cam coupled with a cam-in-block design. The valve 12 may be either an exhaust valve or an intake valve and has a stem 18 that slides within a shaft 26 in the cylinder head 28 of the engine. The valve 12 is default biased into non-permanent abutment with a valve seat (not shown) by a spring 30. In this view, a primary cam 50 of the primary camshaft (not shown) provides the normal operating function for the full cycle of the valve event. A rocker arm 40 pivots about an axis 46 which is substantially equidistant between a first end 42 and a second end 44 of the rocker arm. A secondary cam 70 rotating about the axis 71 of a secondary camshaft (not shown) is operatively engaged with a substantially vertically traversing push rod 75 via an optional cam roller 73. Push rod 75 and secondary camshaft 70 are contained within a secondary shaft 74 and cavity 78, respectively, in the engine block 80. The phase angle of the secondary camshaft is controlled by the phasing device (not shown). As explained above with respect to the embodiment of Figure 1, when the phasing device varies the

phase angle between the primary and secondary camshafts the secondary cam 70 is out of phase with the primary cam 50. The secondary cam 70 urges the push rod 75 to prevent the rocker arm 40 from allowing the closing of the valve 12 for an extended duration of time as dictated by the phase angle differential. Although this example shows the primary cam as being in the overhead position, the primary cam may be located in the engine block 80 and the secondary cam may be located in the overhead position.

Figure 4 shows a schematic representation of a variation of the valvetrain configuration of Figure 3. In this case, both the primary and secondary camshafts are located within cavities 78 in the engine block 80. Either camshaft may be the primary as required by design consideration.

Figure 5 shows a schematic variation of the valvetrain of Figure 4. In this embodiment, both cams act upon the same end of the pivoting rocker arm 40. However, the primary cam 50 and the secondary cam 70 either directly contact the rocker arm 40 or transmit movement to the rocker arm through cam rollers 73. Further, as with other valvetrain arrangements, either the cam closest to the pivot point 46 may be the primary cam device or the cam nearest the second end 44 of the rocker 40 may be the primary device.

A variation on the valvetrain arrangements described above is shown in Figure 6. This is an end-pivot rocker arm valvetrain. The end of the valve stem 18 contacts the rocker arm 40 in proximity to the first end 42 of the rocker arm. Instead of a pivot point near the center of the rocker arm, the rocker arm pivots in proximity to its second end 44 at a point of contact with one end of a lash adjuster 90. The lash adjuster 90 may be either hydraulically or mechanically driven and continuously adjusts for variations in the seating of the valve 12 in its valve seat (not shown) by wearing of the components of the valvetrain over time. In this schematic, the primary cam 50 is shown to be substantially overhead the valve stem 18 in proximity to the first end 42 of the rocker arm 40 and the secondary cam 70 contacts the rocker arm at a point substantially equidistant from the first end 42 and the second end 44. In this example, an optional cam roller 73 provides the interface between the cam 70 and the rocker arm 40. However, depending on the design requirements of the specific engine on which the valve duration control device is installed,

the positions of the primary and secondary cams can be reversed from what is shown in this Figure.

Some engine designs utilize a bucket tappet 95 as an interface between the end of the valve stem 18 and the rocker arm 40, as shown in the schematic drawing of Figure 7. The rocker arm in this example pivots at its second end 44 at a point of contact with a mechanical or hydraulic lash adjuster 90. Both the primary cam 50 and the secondary cam 70 contact the upper surface of the rocker arm 40. Secondary cam 70 contacts an optional cam roller 73. Primary cam 50 is not shown to contact a cam roller, but one may be provided, as design requirements may dictate. Further, as with the previously described valvetrain arrangements, the positions of the primary and secondary cams may be reversed from what is shown in this Figure.

Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.